Multilayer, oriented film capable of structuring by means of electromagnetic radiation and composed of thermoplastic polyester, for the production of selectively metallized films

ABSTRACT

The invention relates to a multilayer, oriented film, in which at least one layer comprises a polyester which comprises an additive which, on irradiation with electromagnetic radiation, forms metal nuclei on which further metal can be deposited in further steps of the process. The invention further relates to a process for the production of this film and to its use in printed circuit boards, ribbon cables, smart cards, RFID labels, membrane keyboards, and film-based circuits of any type.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to German Patent Application 103 44 513.7, filed Sep. 24, 2003, hereby incorporated herein in its entirety.

FIELD OF THE INVENTION

The invention relates to a multilayer, oriented film, in which at least one layer comprises a polyester which comprises an additive which, on irradiation with electromagnetic radiation, forms metal nuclei on which further metal can be deposited in further steps of the process. The invention further relates to a process for the production of this film and to its use in printed circuit boards, ribbon cables, smart cards, RFID labels, membrane keyboards, and film-based circuits of any type.

BACKGROUND OF THE INVENTION

The use of polyester films for electrical insulation applications is prior art. The ever-more-stringent requirements relating to complexity of the circuits within a small space, together with the need to be able to produce these circuits rapidly, flexibly, and at low cost places stringent technological requirements on the film and on the steps within further processing.

Conventional processes for producing flexible circuits mostly relate to the full-surface metalization of the film web or lamination of the film web to metal foil and subsequent structuring of the resultant conductive surfaces by various processes, e.g. etching or mechanical removal of the undesired quantities of metal. There are also processes in which an embossment/print is applied to the metal, or a conductive paste composed of carbon/silver is applied. Disadvantages of these processes lie in their low flexibility and precision, which results in a relatively large separation between the conductor tracks, and/or the high costs associated with these processes, and/or the low production rates.

EP-A-1 274 288 describes a process in which laser irradiation is used to form copper nuclei from copper-containing metal oxides, and a subsequent electroplating step deposits further copper on the nuclei. That specification describes exclusively injection-molded parts, and there is no indication as to how and whether the process can be applied to polyester films and films generally. In particular, there is no indication of the nature of the polymers and additives needed to permit production of oriented films. The PBT/SiO₂/spinel compounded material described in EP-A-1 274 288 is unsuitable for producing oriented films because the high crystallization rate of the polybutylene terephthalate used and the high level of filling with fumed silica prevent reliable processing of this polymer.

In particular, there is no indication as to how it is possible to produce a film with adequate dimensional stability under conditions of local heating after irradiation with electromagnetic radiation and further processing.

SUMMARY OF THE INVENTION

It was an object of the present invention to provide a film which does not have the disadvantages mentioned and which comprises a compound activatable by radiation which forms metal nuclei on which further metal can be accumulated in further steps of the process. A further object was that this film not only has low production cost and good orientability but also has good mechanical properties, i.e. high longitudinal and transverse tensile strength, high longitudinal and transverse modulus of elasticity, high longitudinal and transverse elongation at break, and high longitudinal and transverse tensile stress to generate a tensile strain of 5% (F5 value), together with, where appropriate, defined shrinkage.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graphical illustration of an exemplary particle size distribution curve.

DETAILED DESCRIPTION OF THE INVENTION

This object is achieved via a multilayer, at least monoaxially stretched polyester film with a total thickness of from 5 to 500 μm (preferably from 12 to 200 μm and particularly preferably from 30 to 150 μm) which comprises, in at least one layer, a metal compound capable of activation via electromagnetic radiation, its amount preferably being from 0.1 to 15% by weight (particularly preferably from 1.0 to 10% by weight and very particularly preferably from 2.0 to 8.0% by weight), based on the total weight of the modified layer.

A metal compound capable of activation by radiation is a metal-containing (inorganic or organic) compound which as a consequence of absorbing electromagnetic radiation liberates metal in elemental form in a chemical reaction. This chemical reaction can also involve other reactants. It is also possible that the electromagnetic radiation is not directly absorbed by the metal-containing compound but by other substances which then transfer the absorbed energy to the metal-containing compound and thus bring about the liberation of elemental metal. The electromagnetic radiation may be UV light (wavelength from 100 to 400 nm), visible light (wavelength from 400 to 800 nm), or infrared light (wavelength from 800 to 25 000 nm), the use of infrared light being preferred. Other preferred forms of radiation are X-ray, gamma, and particle beam (electron beam, α-radiation, and β-radiation).

The accumulation of further metal onto the metal nuclei generated by electromagnetic radiation preferably takes place via electroplating (solution chemistry) processes.

Good capability for orientation includes excellent capability of the film, during its production, to undergo monoaxial or biaxial orientation without break-offs.

The good mechanical properties include, inter alia, high modulus of elasticity in at least one film direction (longitudinal direction (MD) and/or transverse direction (TD)) of greater than 500 N/mm², preferably greater than 2000 N/mm², and particularly preferably greater than 4000 N/mm², and also high tensile strength values in at least one film direction (longitudinal direction (MD) and/or transverse direction (TD)) of greater than 50 N/mm², preferably greater than 100 N/mm², and particularly preferably greater than 150 N/mm², and high elongation at break values in at least one film direction (longitudinal direction (MD) and/or transverse direction (TD)) of greater than 10%, preferably greater than 40%, and particularly preferably greater than 80%.

In one preferred embodiment, the shrinkage of the inventive film at 200° C. is not greater than 25% in any film direction (neither MD nor TD). Indeed, shrinkage at 200° C. is preferably smaller than 15%, and particularly preferably smaller than 5%.

The inventive multilayer film is based on polyesters. The main polymer constituent present in particular in the base layer, but also in the outer and/or intermediate layers, is a polyester (i.e. to an extent of from 55 to 100% by weight, preferably from 70 to 100% by weight, and particularly preferably from 90 to 100% by weight, based on the weight of the respective layer).

According to the invention, a polyester is

-   -   a homopolyester,     -   a copolyester,     -   a blend of various polyesters, and these may be used either in         the form of pure polymers or else in the form of polyesters         comprising recycled material.

Polyesters contain repeat units which derive from dicarboxylic acids (100 mol %) and from diols (likewise 100 mol %). The inventive polyesters are preferably based on terephthalic acid or 2,6-naphthalene-dicarboxylic acid as dicarboxylic acid and on ethylene glycol as diol.

In particular, the inventive polyesters contain from 10 to 100 mol % of terephthalate or from 10 to 100 mol % of 2,6-naphthalate as dicarboxylic acid components (the total amount of dicarboxylic acid components making up 100 mol %). Other dicarboxylic acid components which may be present in the inventive polyester are from 0 to 50 mol % of 2,6-naphthalate (if terephthalate is used as main component), from 0 to 50 mol % of terephthalate (if naphthalate was used as main component), from 0 to 20 mol % of isophthalate (preferably from 0.5 to 4 mol %), and also from 10 to 60 mol % of 4,4′-diphenyl-dicarboxylate. Other dicarboxylic acid components, such as 1,5-naphthalenedicarboxylate, should not exceed a proportion of 30 mol %, preferably 10 mol %, in particular 2 mol %.

As diol component, the inventive polyester contains from 10 to 100 mol % of ethylene glycol (EG) (the entire amount of diol components making up 100 mol %). The proportion of diethylene glycol should not exceed 10 mol %, and is ideally from 0.5 to 5 mol %. Other diol components, such as cyclohexanedimethanol, 1,3-propanediol, 1,4-butanediol should not exceed a proportion of 50 mol %, their proportion preferably being less than 30 mol %, particularly preferably less than 10 mol %.

The polyester composition of functional outer layers may deviate from what has been described above, and is described by way of example in the paragraph concerning sealable outer layers below.

Besides the specified main polymer constituents, other embodiments of the film layers may contain up to 45% by weight (preferably up to 30% by weight, particularly preferably up to 20% by weight, based on the weight of the respective film layer) of other polymers, such as polyetherimides (e.g. ®Ultem 1000 from GE Plastics Europe, NL), polycarbonate (e.g. ®Makrolon from Bayer, DE), polyolefins, such as COCs (e.g. ®Topas from Ticona, DE), polyamides (®Ultramid from BASF, DE), etc.

The polyesters are generally prepared by processes known from the literature from the dicarboxylic acid or dicarboxylic ester and the diols mentioned. The polyesters may either be prepared by the transesterification process using the usual catalysts, e.g. salts of Zn, or Ca, of Li, or of Mn, or by the direct esterifiction process.

The inventive multilayer film is composed of a base layer B, of at least one outer layer A or C, and, where appropriate, of further intermediate layers, preference in particular being given to a three-layer A-B-A or A-B-C structure. For these embodiments, it is advantageous for the polymer of the base layer B to have a melt viscosity similar to that/those of the outer layer(s) adjacent to the base layer.

In one preferred embodiment, the functional layer C is sealable. This sealable outer layer applied via coextrusion to the base layer B has a structure based on polyester copolymers. For the purposes of the invention, two variants are preferred here.

-   a: Copolyester composed of terephthalic acid and isophthalic acid -   b: Copolyester composed of terephthalic acid and     naphthalenedicarboxylic acid     Variant a:

The polymer of the sealable outer layer is composed of copolyesters composed mainly, i.e. to an extent of at least from 75 to 95 mol %, of isophthalic acid components and terephthalic acid components in the dicarboxylic acid category, and from 70 to 95 mol % of ethylene glycol components in the diol category. The remaining monomer units derive from the other aliphatic, cycloaliphatic, or aromatic diols and, respectively, dicarboxylic acids which may also occur in the base layer. The preferred copolyesters, which provide the desired sealing properties, are those whose structure is composed of ethylene terephthalate components and ethylene isophthalate components. The proportion of ethylene terephthalate is from 40 to 95 mol %, and the corresponding proportion of ethylene isophthalate is from 60 to 5 mol %. Preference is given to copolyesters in which the proportion of ethylene terephthalate is from 50 to 90 mol % and the corresponding proportion of ethylene isophthalate is from 50 to 10 mol %, and very particular preference is given to copolyesters in which the proportion of ethylene terephthalate is from 60 to 85 mol % and the corresponding proportion of ethylene isophthalate is from 40 to 15 mol %.

Variant b:

The polymer of the sealable outer layer is composed of copolyesters composed mainly, i.e. to an extent of at least from 75 to 95 mol %, of naphthalenedicarboxylic acid components and terephthalic acid components in the dicarboxylic acid category, and of ethylene glycol components in the diol category. The remaining monomer units derive from the other aliphatic, cycloaliphatic, or aromatic diols and, respectively, dicarboxylic acids which may also occur in the base layer. The preferred copolyesters, which provide the desired sealing properties, are those whose structure is composed of ethylene terephthalate components and ethylene naphthalate components. The proportion of ethylene terephthalate is from 30 to 75 mol %, and the corresponding proportion of ethylene naphthalate is from 70 to 25 mol %. Preference is given to copolyesters in which the proportion of ethylene terephthalate is from 40 to 60 mol % and the corresponding proportion of ethylene naphthalate is from 60 to 40 mol %. If the content of polyethylene naphthalate (PEN) in the sealable layer is inadequate to achieve the inventive total content of PEN in the film layer, the balancing PEN content required should advantageously be added to the base layer, and a PEN-free outer layer should advantageously be applied.

Variants a and b may be combined with one another. The minimum amounts of isophthalic acid (IPA) and, respectively, PEN can thus be reduced. However, for PET/PEN/polyethylene isophthalate sealable layers (PET=polethylene terephthalate) it has proven advantageous for the PEN content of the sealable layer to be at least 15% by weight and the polyethylene isophthalate content to be at least 5% by weight.

The thickness of the outer layer(s) is selected independently of the other layers and is preferably in the range from 0.1 to 10 μm, in particular from 0.2 to 5 μm, with preference from 1 to 3 μm, and the thickness and composition of outer layers applied here on the two sides may be identical or different. The thickness of the base layer is correspondingly calculated from the difference between the total thickness of the film and the thickness of the outer and intermediate layer(s) applied, and can therefore, like the total thickness, vary within wide boundaries.

The compound capable of activation by radiation is composed of electrically non-conductive high-thermal-stability organic or inorganic metal compounds which are preferably not soluble and stable in aqueous acidic or alkaline metalizing baths. Particularly suitable compounds are those which have maximum light absorption, in particular in the IR region. Compounds of this type are described in EP-A-1 274 288. Preference is given here to compounds of metals of the d- and f-group of the Periodic Table of the Elements with non-metals. The metal-containing compounds are particularly preferably metal oxides, in particular monooxides of the d-metals of the Periodic Table of the Elements. Higher metal oxides are particularly suitable. In one particularly preferred embodiment of the invention, the higher oxides are spinels, in particular copper-containing spinels, such as CuCr₂O₄. Suitable copper-containing spinels are commercially available, an example being PK 3095 from Ferro (DE) or 34E23 or 34E30 from Johnson Matthey (DE).

The concentration of these compounds present in the inventive film is from 0.1 to 15% by weight, preferably from 1.0 to 10% by weight and particularly preferably from 2.0 to 8.0% by weight. This total concentration may be distributed here over two or more layers of the film, but the entire amount is preferably added to the outer layers, preferably to one of the outer layers.

If the metal-containing compound is not soluble in the polyester used for the production of the film, the particles have an average size (d₅₀ value) of from 0.01 to 20 μm, preferably from 0.05 to 10 μm, and particularly preferably from 0.1 to 5 μm.

It was more than surprising here that the use of the compound described and capable of activation by radiation for exclusive modification of the film's outer layer(s), which is/are thin in relation to the total thickness of the film, is fully sufficient to obtain a film capable of structuring via electromagnetic radiation and suitable for the applications mentioned. A particular economic advantage here is that the total amount of the compound capable of activation by radiation needed for the production of the inventive film is considerably smaller than when the base layer is also modified or the entire film is modified.

One or more layers of the inventive film may comprise further particulate additives, such as fillers and antiblocking agents. Typical fillers and antiblocking agents are inorganic and/or organic particles, such as silocon dioxide (precipitated or fumed), calcium carbonate, magnesium carbonate, barium carbonate, calcium sulfate, barium sulfate, lithium phosphate, calcium phosphate, magnesium phosphate, titanium dioxide (rutile or anatase), kaolin (hydrated or calcined), aluminum oxide, aluminum silicates, lithium fluoride, the calcium, barium, zinc, or manganese salts of the dicarboxylic acids used, or crosslinked polymer particles, e.g. polystyrene or polymethyl methacrylate particles.

It is also possible to select mixtures of two or more of the abovementioned particle systems or mixtures of particle systems with the same chemical composition but different particle size. The particles are advantageously added to the polyester before melting begins.

If a layer of the film comprises further particulate additives, the total concentration of these particles is less than 30% by weight, based on the total weight of the modified layer, preferably less than 25% by weight, and particularly preferably less than 20% by weight.

The particulate additives have an average size (d₅₀ value) of from 0.01 to 15 μm, preferably from 0.03 to 10 μm, and particularly preferably from 0.05 to 1 μm. In one preferred embodiment, the proportion of particles with d₅₀>3 μm is smaller than 2000 ppm, and particularly preferably <1000 ppm.

It has been found that even films without other additives (other than the active metal component) can be used in the invention. However, formation of the metal nuclei is improved if at least one layer of the film comprises silicon dioxide as filler within the particle sizes and amounts mentioned above. For the formation of the metal nuclei, it has proven particularly advantageous for the film layer(s) modified with the component capable of activation by radiation also to comprise from 0.1 to 30% by weight, preferably from 0.5 to 25% by weight, and particularly preferably from 1 to 20% by weight (based on the total weight of the modified layer) of silicon dioxide particles with d₅₀<1 μm.

The inventive film may comprise other additives, such as UV stabilizers, flame retardants, hydrolysis stabilizers, and antioxidants.

In another embodiment, at least one layer of the inventive film is flame-retardant. Flame-retardant means that in what is known as a fire protection test to UL94 VTM the film achieves at least the classification VTM-2. The film then comprises, in one or more layers, a flame retardant at a concentration in the range from 0.2 to 30% by weight, preferably from 0.5 to 25% by weight, particularly preferably from 1.0 to 20% by weight, based on the weight of the modified layer. It is important that the flame retardant is soluble in the polyester, because otherwise the required mechanical properties are not achieved. Examples of suitable flame retardants are organic bromine, chlorine, or nitrogen compounds, or metal hydroxides or metal oxide trihydrates. However, the halogen compounds have the disadvantage that toxic and corrosive hydrogen halides are produced in the event of a fire. Another disadvantage is the low light-resistance of a film equipped therewith. Examples of other suitable flame retardants are organophosphorus compounds, such as carboxyphosphinic acids, their anhydrides, and dimethyl methanephosphonate. Very suitable flame retardants here are those in which the phosphorus compound has chemical bonding to the polyester. Very particular preference is given to bis(2-hydroxyethyl) [(6-oxido-6H-dibenzo[c,e][1,2]oxaphosphorin-6-yl)methyl]butanedicarboxylate of the formula

In this preferred embodiment, the inventive low-flammability film comprises, besides the polyester, the compound capable of activation by radiation, and, if appropriate, particulate additives, from 1 to 20% by weight of an organophosphorus compound as flame retardant soluble in the polyester.

Because the flame retardants generally have some susceptibility to hydrolysis, it may be advisable to add a hydrolysis stabilizer. Examples of suitable hydrolysis stabilizers are polymeric carbodiimides, e.g. ®Stabaxol P from Rheinchemie (DE). The amount of these used is preferably from 0.1 to 1.0% by weight (based on the weight of the modified layer).

These abovementioned proportions of flame retardant and hydrolysis stabilizer have also proven advantageous when the main constituent of the film is not polyethylene terephthalate but another polyester.

The compound capable of activation by radiation and any other additives used, such as particles, UV stabilizers, flame retardants, hydrolysis stabilizers, and antioxidants, may be added in the form of a glycolic dispersion during the polycondensation process to the polyester used for the production of the inventive film. However, it is preferable to add the component capable of activation by radiation and/or any other additives used by way of masterbatches to the polyester during film extrusion.

The film may also be coated to establish other properties. Particularly typical coatings are coatings with adhesion-promoting, antistatic, slip-improving, or release action. Clearly, these additional layers may be applied to the film by way of in-line coating means of aqueous dispersions after the longitudinal stretching and prior to the transverse stretching.

In one particular embodiment, at least one side of the film has a silicone coating, e.g. as described in U.S. Pat. No. 5,728,339. This embodiment has the advantage that after the laser treatment the surrounding regions have protection from the corrosive action of the electroplating bath, and that residues of the electroplating solution can be removed more easily from the film surface.

For certain applications, it can be advantageous to pretreat the surface of the film chemically, using an acid. For this “adhesion-promoting etch” particularly suitable compounds are trichloroacetic acid, dichloroacetic acid, or hydrofluoric acid, which act on the surface for a short time (from 5 to 120 seconds) and then are removed by means of an air knife. This gives the film a very reactive, amorphous surface.

The additives, i.e. the metal compound capable of activation by radiation, and also any other fillers and other additives present, may be introduced into the polymer by means of a commercially available twin-screw extruder (e.g. from Coperion). Here, inventive polyester pellets are introduced into the extruder together with the particles/additives and extruded, then quenched in a water bath, and then pelletized.

However, in one preferred process for preparing the inventive polyesters, the additives are added directly during the preparation of the polyester. In the case of the DMT process, the additives are usually added after the transesterification or directly prior to the polycondensation (e.g. by way of the transport line between transesterification and polycondensation vessels) in the form of a glycolic dispersion. However, the addition may also take place prior to the start of the transesterification. In the case of the TPA process, the addition preferably takes place at the start of the polycondensation. However, later addition is also possible. In the case of this process it has proven advantageous to filter the glycolic dispersions through a PROGAF PGF 57 (Hayward Ind. USA) filter prior to addition.

The present invention also provides a process for producing the film. Production usually takes place via an extrusion or coextrusion process known per se. It has proven particularly advantageous to add the component capable of activation by radiation and any other additives used, such as particles, UV stabilizers, flame retardants, hydrolysis stabilizers, and antioxidants, in the form of predried or precrystallized masterbatches, prior to the extrusion process.

In masterbatch technology it is preferable that the particle size and the bulk density of the masterbatches are similar to the particle size and the bulk density of the polyester used, thus achieving homogeneous dispersion, resulting in homogeneous properties.

The polyester films may be produced in the form of a multi-layer film by known processes from a polyester and, if appropriate, from other raw materials, at least one component capable of activation by radiation, and also, if appropriate, other additives.

Masterbatches which comprise the component capable of activation by radiation have preferably been pre-crystallized and/or predried. The same applies to masterbatches which comprise particles, UV stabilizer(s), flame retardants, and/or other additives. The predrying includes progressive heating of the masterbatches under reduced pressure (from 20 to 80 mbar, preferably from 30 to 60 mbar, in particular from 40 to 50 mbar), with stirring, and, if appropriate, afterdrying at a constant elevated temperature (likewise under reduced pressure). It is preferable for the masterbatch to be charged batchwise at room temperature from a feed vessel in the desired blend together with the polyester and, if appropriate, with other raw material components into a vacuum dryer in which the temperature profile moves from 10 to 160° C., preferably from 20 to 150° C., in particular from 30 to 130° C., during the course of the drying time or residence time. During the residence time of about 6 hours, preferably 5 hours, in particular 4 hours, the raw material mixture is stirred at from 10 to 70 rpm, preferably from 15 to 65 rpm, in particular from 20 to 60 rpm. The resultant precrystallized or predried raw material mixture is post-dried in a downstream vessel, likewise evacuated, at temperatures of from 90 to 180° C., preferably from 100 to 170° C., in particular from 110 to 160° C., for from 2 to 8 hours, preferably from 3 to 7 hours, in particular from 4 to 6 hours.

In the preferred coextrusion process for the production of the film, the melts corresponding to the individual layers of the film are coextruded through a flat film die and quenched in the form of a substantially amorphous prefilm on a chill roll. This film is then reheated and oriented in at least one direction—either in machine direction (MD) or in transverse direction (TD)—however preferably longitudinally and transversely, or transversely and longitudinally, or longitudinally, transversely, and again longitudinally and/or transversely. The film temperatures in the stretching process are generally above the glass transition temperature Tg of the polyester used by from 10 to 60° C., and the longitudinal stretching ratio is usually from 2.0 to 6.0, in particular from 3.0 to 4.5, the transverse stretching ratio usually being from 2.0 to 5.0, in particular from 3.0 to 4.5, the ratio for any second longitudinal and transverse stretching carried out usually being from 1.1 to 5.0. The first longitudinal stretching may also be carried out simultaneously with the transverse stretching (simultaneous stretching). The heat-setting of the film follows at oven temperatures of from 180 to 260° C., in particular from 220 to 250° C. The film is then cooled and wound.

In one preferred embodiment, the heat-setting takes place at from 220 to 250° C., and the film is relaxed transversely at this temperature by at least 1% (preferably at least 2%).

In another preferred embodiment, the heat-setting takes place at from 220 to 250° C., and the film is relaxed transversely at this temperature by at least 1% (preferably at least 2%), and then again transversely relaxed, again by at least 1% (preferably at least 2%) at temperatures of from 180 to 150° C. in the cooling phase.

In another preferred embodiment, the film is stretched in MD and TD by a factor of at least 3.0, this stretching taking place in a simultaneous frame. The heat-setting takes place at from 220 to 250° C., and the film is longitudinally and transversely relaxed by at least 1% at this temperature.

The inventive multilayer films have the required good mechanical properties. For example, the modulus of elasticity in at least one film direction (longitudinal (MD) and/or transverse (TD)) is at least 500 N/mm², preferably greater than 2000 N/mm², and particularly preferably greater than 4000 N/mm². The tensile strength values in at least one film direction (longitudinal (MD) and/or transverse (TD)) is greater than 50 N/mm², preferably greater than 100 N/mm², and particularly preferably greater than 150 N/mm². The elongation at break values in at least one film direction (longitudinal direction (MD) and/or transverse direction (TD)) is greater than 10%, preferably greater than 40%, and particularly preferably greater than 80%.

The shrinkage of the inventive multilayer film at 200° C. is not greater than 25% in any film direction (neither MD nor TD). Indeed, shrinkage at 200° C. is smaller than 15%, and preferably smaller than 5%.

It was more than surprising that use of the additives described, combined with the preferred predrying and/or precrystallization of the raw materials and with the process conditions described can produce, without technical problems (such as caking in the dryer or break-offs) a film which has the required property profile and is capable of activation by electromagnetic radiation. During the production process, no, or hardly any, deposits on the dies or evolution of gasses were observed, the result being that the inventive film has excellent mechanical properties, excellent optical properties, an excellent profile, and excellent layflat. It has excellent capability for orientation, and can therefore be produced reliably and cost-effectively.

It is moreover very surprising that it is also possible to reuse the recycled material without adversely affecting the mechanical properties of the film. Within the bounds of accuracy of measurement, there is no adverse effect on mechanical properties even in comparison with an unmodified film.

The combined properties of the inventive films make them suitable for a wide variety of applications, for example for printed circuit boards, ribbon cables, smart cards, RFID labels, membrane keyboards, and film-based circuits of any type.

The invention is further illustrated below using examples, but is not restricted thereto.

The individual properties were measured here to the following standards or by the following methods:

Test Methods

Mechanical Properties

Modulus of elasticity, tensile strength, elongation at break, and F5 value are measured longitudinally and transversely to ISO 527-1-2 with the aid of tensile strain measurement equipment (Zwick 010, Ulm, DE).

Shrinkage

Thermal shrinkage was determined on square film samples with an edge length of 10 cm. The samples were measured precisely (edge length L_(o)) and heat-conditioned for 15 minutes at 200° C. in a convection oven. The specimens were removed and measured precisely at room temperature (edge length L). Shrinkage is given by the equation shrinkage [%]=100·(L ₀ −L)/L Standard Viscosity (SV) and Intrinsic Viscosity (IV)

Standard viscosity was measured—by a method based on DIN 53726—on a 1% strength solution in dichloroacetic acid (DCA) at 25° C. SV (DCA)=(ηrel−1)×1000. Intrinsic viscosity (IV) is calculated as follows from standard viscosity (SV) IV=[η]=6907·10⁻⁴ SV (DCA)+0.063096[dl/g] Measurement of Average Diameter d₅₀

Average diameter d₅₀ was determined by means of a laser on a Malvern Mastersizer by the standard method (an example of other measurement equipment being the Horiba LA 500 or Sympathec Helos, which use the same principle of measurement). For this, the specimens were placed with water in a cell, which was then placed in the measurement equipment. The measurement procedure is automatic and also includes the mathematical determination of d₅₀ values. The d₅₀ value here is defined as the value determined from the (relative) cumulative particle size distribution curve: the point of intersection of the 50% ordinate value with the cumulative curve immediately giving the desired d₅₀ value on the abscissa axis. FIG. 1 provides a graphical illustration of an exemplary particle size distribution and d₅₀ value determination.

Seal Seam Strength

To determine seal seam strength, two film strips of width 15 mm are mutually superposed and sealed at 130° C. with a sealing time of 0.5 s and a sealing pressure of 2 bar, using NDS equipment from Brugger Feinmechanik (Munich, DE), using single-side heated sealing jaw. The sealed surface is about 15×9 mm. Seal seam strength was determined by the T-peel method, with the aid of tensile strain measurement equipment (Zwick 010, Ulm DE). The two strip ends here were clamped into the opposite clips and separated at a velocity of 200 mm/min. The maximum force measured during this process is the seal seam strength, and is stated in N/15 mm.

Film Production

Polyester chips are mixed in the ratio stated in the examples and precrystallized in a fluidized-bed dryer at 155° C. for 1 minute, and then dried for 3 hours in a tower dryer at 150° C., and melted in a single-screw extruder at 290° C. The molten polymer extrudates were brought together in a coextrusion die and drawn off by way of a take-off roll (roll temperature 20° C.). The film was stretched by a factor of 3.5 in the machine direction at 116° C. (film temperature in the stretching gap), and transverse stretching by a factor of 3.2 was carried out in a frame at 110° C. The film was then heat-set at 229° C., and relaxed by 1% transversely at temperatures of from 229 to 200° C., and again relaxed by 1% transversely at temperatures of from 180 to 150° C. The production speed (final film speed) is 300 m/min. The final film thickness is 50 μm.

EXAMPLES

The following raw materials are used in the examples:

Masterbatch MB1:

10% by weight of PK3095 from Ferro and 90% by weight of polyethylene terephthalate (PET)

Masterbatch MB2:

10% by weight of PK3095 from Ferro (Germany) and 90% by weight of polybutylene terephthalate (PBT)

Masterbatch MB3:

4% by weight of Aerosil TT600 SiO₂ particles from Degussa (Germany) (d₅₀ of agglomerates about 300 nm; primary particle d₅₀ about 50 nm) and 96% by weight of polyethylene terephthalate (PET)

Masterbatch MB4:

4% by weight of Aerosil TT600 SiO₂ particles from Degussa (Germany) (d₅₀ of agglomerates about 300 nm; primary particle d₅₀ about 50 nm) and 96% by weight of polybutylene terephthalate (PBT)

Masterbatch MB5:

4% by weight of Omyacarb BP CaCo₃ particles from Omya (USA) (d₅₀ of particles 22 μm) and 96% by weight of polyethylene terephthalate (PET)

Masterbatch MB6:

10% by weight of PK3095 from Ferro (Germany) and 90% by weight of polyethylene naphthalate (PEN)

Masterbatch MB7:

4% by weight of Aerosil TT600 SiO₂ particles from Degussa (Germany) (d₅₀ of agglomerates about 300 nm; primary particle d₅₀ about 50 nm) and 96% by weight of polyethylene naphthalate (PEN)

Masterbatch MB8:

Masterbatch MB8 comprises 6% by weight of M-Ester from Sanko Co. Ltd. (CAS No. 63562-34-5) and 94% by weight of polyethylene terephthalate from KoSa (Germany).

Polymer P1:

100% by weight of RT49 polyethylene terephthalate from KoSa (Germany).

Polymer P2:

25% by weight of Aerosil 90 from Degussa (Germany), 5% by weight of PK3095 from Ferro (Germany), and 70% by weight of polybutylene terephthalate (PBT)

Polymer P3:

100% by weight of polybutylene terephthalate

Polymer P4:

100% by weight of polyethylene naphthalate

Polymer P5:

18% by weight of Blanc-fixe XR-SU barium sulfate from Sachtleben (Germany), 0.03% by weight of Hostalux KS optical brightener from Clariant (Germany), 81.97% by weight of RT49 polyethylene terephthalate from KoSa (Germany)

Polymer P6:

100% by weight of copolyester composed of 78 mol % of ethylene terephthalate and 22 mol % of ethylene isophthalate (prepared via transesterification in the presence of a manganese catalyst, manganese concentration: 100 ppm)

Example 1

An ABA film was produced as stated above with a base layer thickness of 46 μm and outer layers A each of 2 μm.

Polymer mixture for outer layers A: 50% by weight of MB1; 25% by weight of MB3; 25% by weight of P1

Polymer mixture for base layer B: 100% by weight of P1

Properties of the film can be found in Table 1.

Example 2

Example 1 was repeated. However, recycled material produced from the film of example 1 was also added to the base layer B.

Polymer mixture for outer layers A: 50% by weight of MB1; 25% by weight of MB3; 25% by weight of P1

Polymer mixture for base layer B: 50% by weight of P1; 50% by weight of recycled material

Properties of the film can be found in Table 1.

Example 3

Example 1 was repeated.

Polymer mixture for outer layers A: 50% by weight of MB1; 50% by weight of P1

Polymer mixture for base layer B: 100% by weight of P1

Properties of the film can be found in Table 1.

Example 4

An ABC film was produced as stated above with a base layer thickness of 46 μm and outer layers A and C each of 2 μm.

Polymer mixture for outer layer A: 50% by weight of MB1; 25% by weight of MB3; 25% by weight of P1

Polymer mixture for base layer B: 100% by weight of P1

Polymer mixture for outer layer C: 25% by weight of MB3; 75% by weight of P1

Properties of the film can be found in Table 1.

Example 5

Example 1 was repeated.

Polymer mixture for outer layer A: 50% by weight of MB1; 25% by weight of MB3; 25% by weight of P1

Polymer mixture for base layer B: 25% by weight of MB3; 75% by weight of P1

Properties of the film can be found in Table 1.

Example 6

Example 1 was repeated.

Polymer mixture for outer layer A: 50% by weight of MB1; 25% by weight of MB3; 25% by weight of P1

Polymer mixture for base layer B: 100% by weight of P5

Properties of the film can be found in Table 1.

Example 7

Example 1 was repeated.

Polymer mixture for outer layer A: 50% by weight of MB1; 25% by weight of MB3; 25% by weight of P1

Polymer mixture for base layer B: 25% by weight of MB8; 75% by weight of P1

The film was subjected to a UL94 VTM fire test and achieved fire classification VTM-0. Other properties of the film can be found in Table 1.

Example 8

Example 1 was repeated.

Polymer mixture for outer layer A: 50% by weight of MB6; 25% by weight of MB7; 25% by weight of P4

Polymer mixture for base layer B: 85% by weight of P1; 15% by weight of P4

Properties of the film can be found in Table 1.

Example 9

Example 1 was repeated.

Polymer mixture for outer layer A: 50% by weight of MB2; 25% by weight of MB3; 25% by weight of P1

Polymer mixture for base layer B: 100% by weight of P1

Properties of the film can be found in Table 1.

Example 10

An ABC film was produced as stated above with a base layer thickness of 47 μm, an outer layer A of 2 μm, and a sealable outer layer C of 1 μm.

Polymer mixture for outer layer A: 50% by weight of MB1; 25% by weight of MB3; 25% by weight of P1

Polymer mixture for base layer B: 100% by weight of P1

Polymer mixture for outer layer C: 100% by weight of P6

The seal seam strength of the film (side C/side C) was 2.7 N/15 mm. Other properties of the film can be found in Table 1.

Example 11

Example 1 was repeated with different polymer mixtures.

Polymer mixture for outer layer A: 100% by weight of P2

Polymer mixture for base layer B: 100% by weight of P1

Film production was not easy, because occasional break-offs occurred. Furthermore, occasional delamination of the outer layers occurred. Properties of the film can be found in Table 1.

Comparative Example 1

An attempt was made to produce an ABA film with a base layer thickness of 46 μm and outer layers A each of 2 μm as stated above from the polymer R2 (similar to the polymer from the example of EP-A-1 274 288). Polymer mixture for outer layer A: 100% by weight of P2

Polymer mixture for base layer B: 100% by weight of P2

It proved impossible to orient the film, because every attempt at stretching led to break-offs. It was impossible to produce a film.

Comparative Example 2

Example 1 was repeated.

Polymer mixture for outer layer A: 50% by weight of MB1; 25% by weight of MB3; 25% by weight of P1

Polymer mixture for base layer B: 25% by weight of MB5; 75% by weight of P1

Only small amounts of the film could be produced, because break-offs often occurred. Delamination of the outer layers also occurred. Properties of the film can be found in Table 1.

Comparative Example 3

Example 1 was repeated. However, heat-setting did not take place as stated above at 229° C., but at 150° C., and no relaxation took place. Properties of the film can be found in Table 1.

Conductor Track Production:

In the region of the conductor tracks to be applied, the films produced were irradiated by infrared laser radiation generated by a diode-pumped Nd:YAG laser (Microline 3D IR 160 from LPKF AG (Germany)), using an intensity which generates very little ablation, associated with structured metal nucleation. After brief treatment in an ultrasound cleaning bath containing demineralized water, the film is passed through a commercially available chemically reductive copper-plating bath. Here, the conductor tracks are constructed in the irradiated regions.

Results of Conductor Track Production:

The conductor tracks generated were assessed visually by means of an optical microscope (incident light) at 20× magnification. The coherence of the copper layer was evaluated visually, and allocated to the following categories: good, less good, and poor.

TABLE 1 MD TD MD TD modulus modulus MD TD elonga- elonga- of elas- of elas- tensile tensile tion at tion at MD TD Visual Conductor ticity in ticity in strength strength break break shrinkage shrinkage appearance track N/mm² N/mm² in N/mm² in N/mm² in % in % 200° C. 200° C. of film production Example  1 4000 5300 175 260 163 112 4.2 2.1 slightly gray good  2 4100 5400 172 265 164 110 4.3 2.0 slightly gray good  3 4200 5100 177 270 165 105 4.5 2.2 gray less good  4 4300 5300 173 268 160 111 4.2 2.3 slightly gray good  5 4400 5200 169 257 155 100 4.0 2.5 slightly gray good  6 4200 5100 163 240 160 110 4.3 2.4 white good  7 3950 5000 160 225 178 118 4.7 2.7 slightly gray good  8 3800 4900 163 248 172 115 4.8 2.6 slightly gray good  9 4100 5200 165 252 150 105 4.3 2.3 slightly gray good 10 4200 5100 164 241 156 119 4.1 2.2 slightly gray good 11 4100 5300 155 230 40 73 4.2 2.7 slightly gray good*) Comparative example  1 no film no film no film no film no film no film no film no film no film no film obtained obtained obtained obtained obtained obtained obtained obtained obtained obtained  2 4200 5400  32  41  25 39 4.3 2.5 white good  3 4400 5100 140 215 200 120 23 25 slightly gray good**) *)Delamination on the outer layers with the conductor tracks **)Creases formed after laser irradiation 

1. A multilayer, at least monoaxially oriented polyester film with a total thickness of from 5 to 500 μm which comprises a metal compound which on irradiation with electromagnetic radiation liberates a metal in elemental form within the polyester, said film exhibiting a modulus of elasticity in at least one film direction (longitudinal (MD) and/or transverse (TD)) of greater than 500 N/mm².
 2. The polyester film as claimed in claim 1, wherein the amount of the metal compound present in the film is from 0.1 to 15.0% by weight.
 3. The polyester film as claimed in claim 1, which comprises particulate additives.
 4. The polyester film as claimed in claim 3, wherein said particulate additive is silicon dioxide.
 5. The polyester film as claimed in claim 3, wherein said particulate additive has an average particle size, d₅₀, of from 0.01 to 15 μm.
 6. The polyester film as claimed in claim 1, which has a silicone coating on at least one surface.
 7. The polyester film as claimed in claim 1, wherein at least one layer is composed of a polyester which contains, as dicarboxylic acid component, from 10 to 100 mol % of terephthalate, based on the total amount of the dicarboxylic acid components present.
 8. The polyester film as claimed in claim 1, wherein at least one layer is composed of a polyester which contains, as dicarboxylic acid component, from 10 to 100 mol % of 2,6-naphthalate based on the total amount of the dicarboxylic acid components present.
 9. The polyester film as claimed in claim 1, which has tensile strength values in at least one film direction (longitudinal (MD) and/or transverse (TD)) of greater than 50 N/mm².
 10. The polyester film as claimed in claim 1, which has elongation at break values in at least one film direction (longitudinal (MD) and/or transverse (TD)) of greater than 10 N/mm².
 11. The polyester film as claimed in claim 1, which does not have shrinkage greater than 25% at 200° C. in any film direction (MD or TD).
 12. The polyester film as claimed in claim 1, which has at least two layers and is composed at least of one base layer and one outer layer.
 13. The polyester film as claimed in claim 12, wherein the metal compound is present in one of the layers of the multilayer film.
 14. The polyester film as claimed in claim 12, wherein the metal compound is present in the outer layer(s) of the multilayer film.
 15. The polyester film as claimed in claim 12, wherein one of the outer layers is sealable.
 16. The polyester film as claimed in claim 1, which has at least three layers and is composed at least of one base layer and two outer layers.
 17. A process for producing a polyester film as claimed in claim 1, which comprises extruding, together through a slot die, the melts corresponding to the individual layers of the film, where at least one melt comprises metal compound which on irradiation with electromagnetic radiation liberates a metal in elemental form within the polyester, cooling, reheating, and then orienting in at least one direction, and then heat-setting.
 18. Printed circuit boards, ribbon cables, smart cards, RFID labels, membrane keyboards, and film-based circuits comprising a film according to claim
 1. 19. The polyester film as claimed in claim 1, further comprising flame retardant.
 20. The A multilayer, at least monoaxially oriented polyester film with a total thickness of from 5 to 500 μm which comprises a metal compound which on irradiation with electromagnetic radiation liberates a metal in elemental form within the polyester, wherein the metal compound is a metal oxide.
 21. The polyester film as claimed in claim 20, wherein the metal compound is a spinel.
 22. The polyester film as claimed in claim 20, wherein the metal compound is CuCr₂O₄.
 23. Multilayer films comprising a metal compound which on irradiation with electromagnetic radiation liberates metal in elemental form for producing multilayer films, said film exhibiting a modulus of elasticity in at least one film direction (longitudinal (MD) and/or transverse (TD)) of greater than 500 N/mm².
 24. Printed circuit boards, ribbon cables, smart cards, RFID labels, membrane keyboards, and film-based circuits comprising film according to claim
 23. 